The present disclosure relates to an exhaust gas recirculation arrangement. Furthermore, the present disclosure relates to a method for recirculating exhaust gas to an air intake of a power system comprising an internal combustion engine. Additionally, the present disclosure relates to a computer program and/or a control unit.
The present disclosure can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment. Although the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle, but may also be used in other vehicles such as a bus, a work machine or the like.
A power system, for instance a power system for a vehicle, generally has an internal combustion engine (ICE), an exhaust gas system and an intake system. Furthermore, in order to reduce NOx, emissions, a modern power system may also include an exhaust gas recirculation arrangement that feeds a portion of the exhaust oases from the exhaust gas system to the intake system. Such exhaust gas recirculation (EGR) arrangements exist in many different versions, devised to cope with the demanding, and often conflicting requirements imposed upon ICE in their frequently varying operating conditions and by the multitude of purposes that the engines are used for. Among these require tents, one of the most important concerns maintaining a high engine efficiency. At the same time, durability and reliability of a power system are always in focus.
Most modern compression ignition engines, which are used almost exclusively in commercial transport and machinery, make use of turbochargers for higher specific power and reduced fuel consumption. It is known that as regards engine efficiency effect of an exhaust gas recirculation system, it is often an advantage to be able to utilize a so-called “Tong Route EGR” or low-pressure EGR, when the exhaust gas is taken downstream the turbo part of the turbocharger for feeding back to the engine's intake. However, depending on the operating condition of the power system arranged in this way, there may be a risk that liquid droplets, e.g. water droplets, be formed in the exhaust gas recirculation arrangement. Such liquid droplets may impair a portion of the intake system, such as an inlet, air compressor.
In order to mitigate the damaging effect of the liquid droplets, US 2009/0000297 A1 proposes that an, exhaust gas recirculation arrangement be furnished with a condensation separation apparatus separating moisture from that exhaust gas. The thus separated moisture is thereafter directed towards the centre of an intake compressor wheel. Although the US 2009/0000297 A1 exhaust gas recirculation arrangement may result in reduced erosion of a compressor wheel of an intake system, the arrangement may also require a relatively large pressure difference over the arrangement in order for the condensation separation apparatus to be able to operate in a satisfactory manner. Such a large pressure difference may in turn have a negative effect on the engine efficiency.
It is desirable to provide an exhaust gas recirculation arrangement that can mitigate the damaging effect of the liquid droplets possibly formed in the arrangement, in a way that is advantageous for engine efficiency.
As such, the present disclosure relates to an exhaust gas recirculation arrangement for a power system. The power system comprises an internal combustion engine, an exhaust gas system and an intake system comprising an inlet air compressor. The exhaust gas recirculation arrangement comprises a first exhaust gas recirculation path and a second exhaust gas recirculation path for recirculating exhaust gas from the exhaust gas system to the intake system.
Furthermore, according to the present disclosure, the first and second exhaust gas recirculation paths are adapted to recirculate exhaust gas to the same side of the inlet air compressor, in an intended direction of flow of inlet air in the power system. Moreover, the exhaust gas recirculation arrangement comprises a flow controller, preferably the flow controll e comprises a valve connected to the second exhaust gas recirculation path, for controlling the flow volume through at least one of the first and second exhaust gas recirculation paths.
By the provision of an exhaust gas recirculation arrangement that comprises the above-mentioned flow controller, it is possible to selectively control the flow volume of exhaust gas through either one, or both, of the exhaust gas recirculation paths. This in turn implies that one of the exhaust gas recirculation paths can be adapted for handling exhaust gas having a high probability of containing liquid droplets whereas the other recirculation path can be adapted for enabling an appropriate engine efficiency.
Thus, the provision of the two exhaust gas recirculation paths and the flow controller implies that appropriate amounts of exhaust gas may be fed through the respective exhaust gas recirculation path, depending on the operating condition of the power system.
Optionally, the exhaust gas recirculation arrangement comprises a sensor adapted to determine a power system characteristic parameter. The exhaust gas recirculation arrangement is adapted to control the flow controller in response to the power system characteristic parameter.
The above-mentioned sensor implies an appropriate means for determining a relevant power system characteristic which it turn implies an appropriate control of the flow volumes.
Optionally, the power system characteristic parameter is indicative of at least the temperature of the internal combustion engine and/or the liquid content in the exhaust gas produced by the internal combustion engine and/or the liquid content in fluid removed from the exhaust gases by the exhaust gas recirculation arrangement.
A power system characteristic parameter indicative of any one of the above conditions may be suitable for determining how to control the flow volumes through the first and second exhaust vas recirculation paths.
Optionally, the first and second exhaust gas recirculation paths are non-identical. This implies an appropriate possibility to adopt an appropriate flow volume control. The first and second exhaust gas recirculation paths may be non-identical in a plurality of ways. Purely by way of example, the first and second exhaust gas recirculation paths may be physically different, e.g. having different lengths and/or cross-sectional areas. Moreover, the first and second exhaust gas recirculation paths may discharge exhaust gases at different positions and/or in different directions in the intake system.
Optionally, in use, the first exhaust gas recirculation path is associated with a first liquid removal capability and the second exhaust gas recirculation path is associated with a second liquid removal capability, the first liquid removal capability being higher than the second liquid removal capability. In other words, if gas with the same liquid content is fed from the exhaust gas system to the intake system via the first and second exhaust gas recirculation paths, the gas that exits the first exhaust gas recirculation paths will generally have a lower liquid content than the gas exiting the second exhaust gas recirculation paths.
The different liquid removal capabilities imply a possibility to control the flow volume through an exhaust gas recirculation path with an appropriate liquid removal capability, e.g. depending on characteristics of the exhaust gas circulated. Purely by way of example, the second liquid removal capability may be zero or close to zero indicating that the second exhaust gas recirculation path is associated with no. or at least a limited, liquid removal capability.
Optionally, the exhaust gas recirculation arrangement comprises a liquid separator comprising a first and a second gas outlet, the first gas outlet being in fluid communication with the first exhaust gas recirculation path and the second gas outlet being in fluid communication with the second exhaust gas recirculation path.
Having a separator with two outlets implies that the two exhaust gas recirculation paths can be associated with different liquid removal capabilities in a compact manner.
Optionally, the liquid separator comprises a liquid collecting portion and the sensor is located in the liquid collecting portion.
The amount of liquid that is located in, or passes, the liquid collecting portion may be indicative of the liquid content in the exhaust gases. Thus, placing a liquid separator in the liquid collecting portion implies that relevant information as regards the characteristics of the exhaust gas may be determined.
Optionally, the liquid separator comprises a labyrinth section comprising an interior labyrinth portion in fluid communication with the first gas outlet. The labyrinth section implies that the first exhaust gas recirculation path may be associated with a relatively large liquid removal capability.
Optionally, the exhaust gas recirculation arrangement comprises an exhaust gas recirculating conduit adapted to fluidly connect a recirculation inlet, connectable to the exhaust gas system, to the liquid separator.
Optionally, the exhaust gas recirculation arrangement comprises an exhaust gas recirculating cooler located between the recirculation inlet and the liquid separator, as seen in a direction of flow from the recirculation inlet to the liquid separator.
Optionally, the exhaust gas recirculation arrangement further comprises a separator drain conduit adapted to provide a fluid communication between the liquid separator and a drain outlet, connectable to the exhaust gas system. The drain outlet is adapted to be located downstream the recirculation inlet in an intended direction of exhaust gas flow in the exhaust gas system.
The separator drain conduit implies that liquid separated from the recirculated exhaust gases may be fed to the exhaust gases that will not be recirculated. As such, by virtue of the above-mentioned drain conduit separated liquid may be discharged to ambient environment via the exhaust gas system and this in turn implies that the system need not have a separate vessel, such as a tank, for storage of separated liquid.
Optionally, the separator drain conduit comprises a restrictor, preferably the restrictor has a restriction being at least twice the restriction of the first exhaust gas recirculation path.
Optionally, the sensor is located in the separator drain conduit.
Optionally, the exhaust gas recirculation arrangement further comprises a drain check valve for allowing drain flow from the separator to the drain outlet and preventing flow in the opposite direction.
Optionally, the inlet air compressor comprises a radial centre and the first exhaust gas recirculation path is adapted to discharge exhaust gas towards the radial centre. If exhaust gas is directed towards the radial centre of the inlet air compressor, the risk that the flow of exhaust gases will damage, for instance by erosion, the inlet air compressor is relatively low, even if the exhaust gases has a relatively large liquid content.
Optionally, the inlet air compressor comprises a receiving area exposable to inlet air. The first exhaust gas recirculation path being adapted to discharge exhaust gas towards a limited portion, preferably 30% or less, more preferred 15% or less, of the receiving area.
A second aspect of the present disclosure relates to a power system comprising an internal combustion engine and an exhaust gas recirculation arrangement according to the first aspect of the present disclosure.
Optionally, the power system further comprises the exhaust gas system, wherein exhaust gas is adapted to be fed from an exhaust gas feeding portion of the exhaust gas system to the exhaust gas recirculation arrangement. The exhaust gas system further comprises an exhaust pressure governor located downstream of the exhaust gas feeding portion.
Optionally, the exhaust gas system comprises a liquid receiving portion adapted to receive liquid separated by the exhaust gas recirculation arrangement, the liquid receiving portion being located downstream of the exhaust pressure governor.
Optionally, the power system comprises the intake system. The intake system comprises an exhaust gas receiving portion adapted to receive exhaust gas from the first and second exhaust gas recirculation paths. The intake system further comprises an intake flow control valve located upstream the exhaust gas receiving portion.
A third aspect of the present disclosure relates to a vehicle comprising the power system according to the second aspect of the present disclosure and/or an exhaust gas recirculation arrangement according to the first aspect of the present disclosure.
A fourth aspect of the present disclosure relates to a method for recirculating exhaust gas to an air intake of a power system comprising an internal combustion engine, the power system comprises an internal combustion engine, an exhaust gas system and an intake system comprising an inlet air compressor, using a first exhaust gas recirculation path and a second exhaust gas recirculation path. Each one of the first and second exhaust gas recirculation paths is adapted to return exhaust gas to the same side of the inlet air compressor.
The method comprises recirculating exhaust gas from the exhaust gas system to the intake system via at least one of the first and second exhaust gas recirculation paths. Moreover, the method further comprises controlling the flow volume of exhaust gas through at least one of the first and second exhaust gas recirculation paths.
Optionally, the first exhaust gas recirculation path is associated with a first liquid removal capability and the second exhaust gas recirculation path is associated with a second liquid removal capability. The first liquid removal capability is higher than the second liquid removal capability.
Optionally, the method further comprises:
a. determining a power system characteristic parameter and
b. controlling the flow volume of exhaust gas through at least one of the first and second exhaust gas recirculation paths (14, 16) in response to the power system characteristic parameter.
Optionally, the power system characteristic parameter is indicative of at least the temperature of the internal combustion engine and/or the liquid content of the exhaust gas produced by the internal combustion engine and/or the liquid content in fluid removed from the exhaust gases.
Optionally, the method further comprises determining a likelihood of formation of liquid in a portion of the power system, preferably in a liquid separator and/or in a drain conduit of the power system, using the power system characteristic parameter.
Optionally, the method further comprises closing the flow through the second exhaust gas recirculation path (16) if the likelihood of formation of liquid in a portion of the power system exceeds a predetermined threshold level.
Optionally, the method further comprises draining liquid removed from the exhaust vases to a drain outlet located in the exhaust gas system. The method further comprises controlling the exhaust gas pressure upstream the drain outlet such that the exhaust gas pressure exceeds the pressure at the drain outlet by a predetermined amount.
Optionally, the exhaust gas system comprises an exhaust pressure governor and the intake system comprises an intake flow control valve, wherein a predetermined exhaust recirculation flow is achieved by a combined governing of the exhaust pressure governor and the intake flow control valve. The combined governing is controlled for achieving a fuel consumption below a predetermined fuel consumption level.
A fifth aspect of the present disclosure relates to a computer program comprising program code means for performing the steps of the fourth aspect of the present disclosure.
A sixth aspect of the present disclosure relates to a computer readable medium carrying a computer program comprising program code means for performing the steps of the fourth aspect of the present disclosure when the program product is run on a computer.
A seventh aspect of the present disclosure relates to a control unit fir controlling exhaust gas recirculation to an air intake of a power system, the control unit being configured to perform the steps of the fourth aspect of the present disclosure.
Further advantages and advantageous tenures of the invention are disclosed in the following description and in the dependent claims.
It should be noted that the appended drawings are not necessarily drawn to scale and that the dimensions of some features of the present invention may have been exaggerated for the sake of clarity.